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Generator masas in $q$-deformed Araki-Woods von Neumann algebras and factoriality

To any strongly continuous orthogonal representation of $\R$ on a real Hilbert space $\CH_\R$, Hiai constructed $q$-deformed Araki-Woods von Neumann algebras for $-1< q< 1$, which are $W^{\ast}$-algebras arising from non tracial representations of the $q$-commutation relations, the latter yielding an interpolation between the Bosonic and Fermionic statistics. We prove that if the orthogonal representation is not ergodic then these von Neumann algebras are factors whenever $dim(\CH_\R)\geq 2$ and $q\in (-1,1)$. In such case, the centralizer of the $q$-quasi free state has trivial relative commutant. In the process, we study `generator masas' in these factors and establish that they are strongly mixing. The analysis is inspired by a previous work of É. Ricard on Bo$\overset{.}{\text{z}}$ejko-Speicher's factors \cite{ER} and measure-multiplicity invariant of masas introduced by K. Dykema, A. Sinclair and R. Smith in \cite{DSS06}.